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<p>在<a href="initialization.html" title="c/language/initialization">初始化</a><a href="type.html#.E7.B1.BB.E5.9E.8B.E7.BB.84.E5.88.AB" title="c/language/types">标量类型</a>对象时，初始化器必须是单个表达式。
</p><p>标量（包含布尔和枚举类型的整数类型，包含复数和虚数的浮点类型，以及包含指向函数指针的指针类型对象）的初始化器必须是单个表达式，可选地以花括号环绕：
</p>
<table class="t-sdsc-begin">

<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr>
<tr class="t-sdsc">
<td> <code><b>=</b></code> <span class="t-spar">expression</span>
</td>
<td> (1)
</td>
<td class="t-sdsc-nopad">
</td></tr>



<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr>
<tr class="t-sdsc">
<td> <code><b>=</b></code> <code><b>{ </b></code> <span class="t-spar">expression</span> <code><b>} </b></code>
</td>
<td> (2)
</td>
<td class="t-sdsc-nopad">
</td></tr>



<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr></table>
<p>求值该表达式，而其值在<a href="conversion.html" title="c/language/conversion">如同赋值般转换</a>到对象类型后，成为被初始化对象的初值。
</p>
<h3><span class="mw-headline" id=".E6.B3.A8.E6.84.8F">注意</span></h3>
<p>因为应用到转换到规则如同赋值，在确定 <span class="t-spar">expression</span> 所转换到的类型时，忽略被声明类型上的 <a href="const.html" title="c/language/const">const</a> 与 <a href="volatile.html" title="c/language/volatile">volatile</a> 限定符。
</p><p>不使用初始化器时应用的规则见<a href="initialization.html" title="c/language/initialization">初始化</a>。
</p><p>同所有其他初始化，在初始化静态或线程局域<a href="storage_duration.html" title="c/language/storage duration">存储期</a>的对象时， <span class="t-spar">expression</span> 必须为<a href="constant_expression.html" title="c/language/constant expression">常量表达式</a>。
</p><p><span class="t-spar">expression</span> 不能为<a href="operator_other.html#.E9.80.97.E5.8F.B7.E8.BF.90.E7.AE.97.E7.AC.A6" title="c/language/operator other">逗号运算符</a>（除非加括号），因为顶层的逗号会被转译为下个声明器的开始。
</p><p>在初始化浮点类型对象时，对所有拥有自动<a href="storage_duration.html" title="c/language/storage duration">存储期</a>的对象所作的计算如同在执行时进行，并受<a href="../numeric/fenv/FE_round.html" title="c/numeric/fenv/FE round">当前舍入</a>影响；报告 <a href="../numeric/math/math_errhandling.html" title="c/numeric/math/math errhandling"><tt>math_errhandling</tt></a> 中指定的浮点错误。对于拥有静态和线程局域存储期的对象，计算如同在编译时进行，而且不引发异常：
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="c source-c"><pre class="de1"><span class="kw4">void</span> f<span class="br0">(</span><span class="kw4">void</span><span class="br0">)</span>
<span class="br0">{</span>
<span class="co2">#pragma STDC FENV_ACCESS ON</span>
    <span class="kw4">static</span> <span class="kw4">float</span> v <span class="sy1">=</span> <span class="nu19">1.1e75</span><span class="sy4">;</span> <span class="co1">// 不引发异常：静态初始化</span>
 
    <span class="kw4">float</span> u<span class="br0">[</span><span class="br0">]</span> <span class="sy1">=</span> <span class="br0">{</span> <span class="nu19">1.1e75</span> <span class="br0">}</span><span class="sy4">;</span> <span class="co1">// 引发 FE_INEXACT</span>
    <span class="kw4">float</span> w <span class="sy1">=</span> <span class="nu19">1.1e75</span><span class="sy4">;</span>       <span class="co1">// 引发 FE_INEXACT</span>
 
    <span class="kw4">double</span> x <span class="sy1">=</span> <span class="nu19">1.1e75</span><span class="sy4">;</span> <span class="co1">// 可能引发 FE_INEXACT （取决于 FLT_EVAL_METHOD ）</span>
    <span class="kw4">float</span> y <span class="sy1">=</span> 1.1e75f<span class="sy4">;</span> <span class="co1">// 可能引发 FE_INEXACT （取决于 FLT_EVAL_METHOD ）</span>
 
    <span class="kw4">long</span> <span class="kw4">double</span> z <span class="sy1">=</span> <span class="nu19">1.1e75</span><span class="sy4">;</span> <span class="co1">// 不引发异常（转换是准确的）</span>
<span class="br0">}</span></pre></div></div>
<h3><span class="mw-headline" id=".E7.A4.BA.E4.BE.8B">示例</span></h3>
<div class="t-example"><div class="t-example-live-link"><div class="coliru-btn coliru-btn-run-init">运行此代码</div></div>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="c source-c"><pre class="de1"><span class="co2">#include &lt;stdbool.h&gt;</span>
 
<span class="kw4">int</span> main<span class="br0">(</span><span class="kw4">void</span><span class="br0">)</span>
<span class="br0">{</span>
    _Bool b <span class="sy1">=</span> <span class="kw2">true</span><span class="sy4">;</span>
    <span class="kw4">const</span> <span class="kw4">double</span> d <span class="sy1">=</span> <span class="nu16">3.14</span><span class="sy4">;</span>
    <span class="kw4">int</span> k <span class="sy1">=</span> <span class="nu16">3.15</span><span class="sy4">;</span> <span class="co1">// 从 double 转换到 int</span>
    <span class="kw4">int</span> n <span class="sy1">=</span> <span class="br0">{</span><span class="nu0">12</span><span class="br0">}</span>, <span class="co1">// 可选地花括号</span>
       <span class="sy2">*</span>p <span class="sy1">=</span> <span class="sy3">&amp;</span>n,   <span class="co1">// 对自动对象，非常量表达式 OK</span>
       <span class="br0">(</span><span class="sy2">*</span>fp<span class="br0">)</span><span class="br0">(</span><span class="kw4">void</span><span class="br0">)</span> <span class="sy1">=</span> main<span class="sy4">;</span>
    <span class="kw2">enum</span> <span class="br0">{</span>RED, BLUE<span class="br0">}</span> e <span class="sy1">=</span> RED<span class="sy4">;</span> <span class="co1">// 枚举亦是标量类型</span>
<span class="br0">}</span></pre></div></div>
<p><br> 
</p>
</div>
<h3><span class="mw-headline" id=".E5.BC.95.E7.94.A8">引用</span></h3>
<div class="t-ref-std-11">
<ul><li> C11 standard (ISO/IEC 9899:2011): 
</li></ul>
<dl><dd><ul><li> 6.7.9/11 Initialization (p: 140)
</li></ul>
</dd></dl>
<div class="t-ref-std-c99">
<ul><li> C99 standard (ISO/IEC 9899:1999): 
</li></ul>
<dl><dd><ul><li> 6.7.8/11 Initialization (p: 126)
</li></ul>
</dd></dl>
<div class="t-ref-std-c89">
<ul><li> C89/C90 standard (ISO/IEC 9899:1990): 
</li></ul>
<dl><dd><ul><li> 6.5.7 Initialization 
</li></ul>
</dd></dl>
</div></div>
</div>

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